The present invention relates to vehicular auxiliary power systems, such as brake boosters in which the pressure difference between a vacuum and atmospheric pressure is utilized, and more particularly to an arrangement for generating and making available a vacuum in such vehicular auxiliary power systems.
U.S. Pat. No. 3,792,761 describes an arrangement for the generation of vacuum in a brake booster, wherein one chamber of the brake booster is connected to an engine intake system pipe by means of a vacuum conduit. In this arrangement, the brake booster conventionally includes a casing having a diaphragm disposed therein, a piston rod to which the diaphragm is fastened, and a piston return spring. An additional throttle blade, which is actuated by a vacuum switch, is positioned in the air intake pipe of an air filter. The vacuum switch is connected to the brake booster's second chamber, which is pressurized at atmospheric pressure during braking, through a vacuum conduit.
As the brake pedal is depressed, the connecting channel between the two chambers of the brake booster is closed as a result of the displacement of the piston rod. As the piston rod continues its movement, the second chamber is connected to atmosphere, with atmospheric pressure acting on the diaphragm on this side. This causes movement of the diaphragm in opposition to the biasing force of the piston return spring. Concurrently with the pressure increase in the second chamber, the pressure in the vacuum switch is likewise increased, the switch thereby causing closing of the additional throttle blade in the air filter--independent of the position of the carburetor throttle. This results in a boosted vacuum in the engine intake system and, accordingly, in the first chamber of the brake booster. To prevent stopping of the engine, the additional throttle blade includes openings through which the volume of air necessary for idle engine operation is passed into the carburetor.
Normally, the carburetor throttle is so adjusted that the engine reaches its idling speed with the accelerator pedal in the inactive position. On depression of the brake pedal, the additional throttle blade is closed additionally, which is, however, to allow the passage of an amount of air sufficient for idle engine operation. The additional throttle blade remains closed as long as the brake pedal is depressed. The additional throttle blade serves to generate the vacuum only if for some reason the operability of the carburetor's throttle is impaired or if the accelerator pedal and the brake pedal are depressed at the same time. It is not possible to design the additional throttle blade in such a manner that its throttling effect goes beyond that of the carburetor throttle. This would be an offense against many countries' exhaust regulations and would result in an engine stop because of insufficient supply of air. In the event of the carburetor throttle not functioning normally, for example, because of a defect, the arrangement of the additional throttle blade will be an advantage because otherwise it would not be possible to boost the vacuum. The additional throttle blade is, however, only closed on commencement of the braking operation whereupon a sufficient amount of vacuum is generated. The vacuum should, however, be available in the brake booster at the time the braking operation is started to avoid a reduction in the booster effect in the initial phase of the braking operation. Moreover, the additional throttle blade cannot be used to generate a vacuum greater than that produced with the carburetor throttle intact.